<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>异步JS</title>
</head>
<body>
  <script>

    console.log("hello world");
    setTimeout(()=>{
      console.log("123");
    },0)
    console.log("456");
  </script>

</body>
</html>